LED7707 STMicroelectronics, LED7707 Datasheet - Page 34

• Manufacturer Part Number: LED7707
• Description: LED Drivers 6-ROW 85mA LED DRIV BOOST REG LCD PANEL
• Manufacturer: STMicroelectronics

Specifications of LED7707

• High Level Output Current: 85 mA
• Operating Supply Voltage: 4.5 V to 36 V
• Maximum Supply Current: 1 mA
• Maximum Power Dissipation: 2.3 W
• Maximum Operating Temperature: + 150 C
• Mounting Style: SMD/SMT
• Package / Case: VFQFPN-24
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Application information
6.4.5
34/47
T
Equation 35
defining D
Equation 36
The worst case for the output voltage ripple is when input voltage is lower (V
A simple way to select the C
In order to affect as less as possible the current generators, it would be better to fix the
maximum ripple lower than the typical voltage across the generators.
For example considering ΔV
leading generator), the required capacitance is:
Equation 37
A margin from the calculated value should be taken into account because of the
capacitance drop due to the applied voltage when MLCCs are used.
One 10 µF MLCC (or two 4.7 µF MLCCs) can be a good choice for this application.
In case a dimming duty cycle different from 100% is used, a further contribution to the
capacitor discharge (during the off time of the dimming cycle) should be considered.
Input capacitor choice
The input capacitor of a boost converter is less critical than the output capacitor, due to the
fact that the inductor is in series with the input, and hence, the input current waveform is
continuous.
A low ESR capacitor is always recommended.
A capacitor of 10 µF is tentatively a good choice for most of the applications.
OFF
can be calculated as:
2
as:
D
T
2
OFF
=
=
C
2
OUT
OUT
R
T
OUT
⋅
SW
F
0
SW
⋅
lower than 70 mV (i.e. the 10 % of the voltage across the
value is fixing a maximum voltage ripple.
(
⋅
M
>
D
⋅
L
(
−
2
I
, L
⋅
1
=
peak
M
)
2
⎧
⎨
⎩
Δ ⋅
618
569
=
−
⎧
⎨
⎩
V
I
. 0
. 0
OUT
OUT
2 .
7 .
408
376
ns
ns
,
max
)
⋅
T
@
@
OFF
@
@
V
=
V
V
V
IN
IN
. 6
IN
IN
,
,
max
min
,
,
33
max
min
μ
=
=
=
F
=
10
13
10
13
8 .
2 .
8 .
2 .
V
V
V
V
IN,min
= 10.8 V).
LED7707